In many wireless network systems such as Wi-Fi and Bluetooth networks, multiple devices compete for control of a shared communication medium (e.g., Wi-Fi channels). For example, a Wi-Fi network typically includes an access point (AP) in wireless communication with a number of stations (STAs). Because the wireless communication medium is shared by all devices associated with the Wi-Fi network, collisions may occur when multiple devices attempt to transmit data on the medium at the same time. When collisions occur, none of the devices may be able to receive data transmitted by other devices, and the collided data may need to be re-transmitted on the medium. Thus, data collisions on a shared wireless communication medium reduce the overall throughput of the medium, which in turn degrades performance of the wireless network. As the number of devices associated with a wireless network increases, the chances for collisions also increase.
To reduce the occurrence of collisions, the IEEE 802.11 standards define a distributed coordination function (DCF) that instructs individual STAs (and APs) to “listen” to the communication medium to determine when the medium is idle (e.g., using a “carrier sense” technique). Only when a STA detects that the medium has been continuously idle for a DCF Interframe Space (DIFS) duration may it attempt to transmit data on the medium. As a result, for wireless networks having a plurality of associated STAs, a multitude of devices may be listening to the medium at the same time to detect idle periods and thereafter gain access to the medium.
To prevent multiple devices from accessing the medium at the same time, each STA (and/or each AP) may be assigned a random “back-off” period or number. At the end of the DIFS duration, each STA waits for a period of time determined by its back-off number (e.g., its back-off period) before it transmits data on the medium. However, because the quantity of unique back-off numbers is limited, multiple STAs may be assigned the same back-off number, which in turn may result in multiple STAs transmitting data on the medium at the same time. As a result, the assignment of random back-off numbers to STAs (and/or APs) associated with a wireless network may not be sufficient to avoid collisions on the shared medium.